Rubber hose and method for manufacture thereof

ABSTRACT

This invention provides a rubber hose in which an outer rubber layer is laminated by means of extrusion on the outer peripheral surface of an inner rubber layer, wherein: the inner rubber layer is a fluororubber layer  2 ; the outer rubber layer is a reinforcing yarn-woven silicone rubber layer  1  having reinforcing yarns woven therein; an intermediate rubber layer having an adhesive component for the adhesion with the fluororubber layer is provided between the fluororubber layer  2  and the reinforcing yarn-woven silicone rubber layer  1 ; and the intermediate rubber layer is an intermediate silicone rubber layer  3  having a hardness lower than those of the reinforcing yarn-woven silicone rubber layer and the fluororubber layer; and a method for manufacturing the rubber hose. Further, this invention provides a rubber hose in which an outer rubber layer is laminated by means of winding on the outer peripheral surface of an inner rubber layer, wherein: the inner rubber layer is a fluororubber layer  5 ; the outer rubber layer is a fabric-reinforced silicone rubber layer  4 ; an intermediate rubber layer containing an adhesive component for the adhesion with the fluororubber layer  5  is provided between the fluororubber layer  5  and the fabric-reinforced silicone rubber layer  4 ; and the intermediate rubber layer is an intermediate silicone rubber layer  6  having a hardness lower than that of the fabric-reinforced silicone rubber layer; and a method for manufacturing the rubber hose.

TECHNICAL FIELD

The present invention relates to an oil resistant rubber hose throughwhich high-temperature gas passes and a method for manufacturing thesame.

BACKGROUND ART

As is well known, in a vehicle, a rubber hose is connected between aturbocharger and an intercooler, and the intake gas pressurized by thefan in the turbocharger passes through this rubber hose. The fan isdriven by the engine exhaust gas, so that the intake gas reaches a veryhigh temperature. Accordingly, the rubber hose is required to have aheat resistance which can withstand such a high temperature and avibration resistance at such a high temperature. As materials for such arubber hose which is capable of withstanding the above mentioned hightemperature, silicone rubber has hitherto been adopted. However, incurrent turbochargers, the pressurizing force is further increased, andconsequently, the heat resistance required is such that turbochargerscan withstand temperatures of 200° C. or higher.

In addition, the recent implementation of the Japan new short-termexhaust gas regulation of diesel vehicles also requires to install apositive crankcase ventilation system. Accordingly, the above describedrubber hose is also required to have an oil resistance and a resistanceto gas permeation for the purpose of preventing the permeation of theblowby gas. For a rubber hose that is required to have such severe heatand oil resistance, conventional silicone rubber as used alone does notsufficiently meet these requirements, and rubber hoses made of newmaterials are demanded. In this connection, fluororubber attractsattention because it excels in heat resistance, oil resistance and thelike, and an attempt has been made to produce a laminated air hose inwhich the fluororubber is used for the innermost portion thereof (forexample, see Japanese Patent Laid-Open No. 2000-193152).

Japanese Patent Laid-Open No. 2000-193152 describes the structure of alaminated hose made of fluororubber and silicone rubber. However, it isdifficult to obtain a hose having an oil resistance at high temperaturesand a vibration resistance at high temperatures by simply combiningindividual materials on the basis of the properties of the respectivematerials. The critical points of this technique may include:

(1) a problem to develop a method for providing an adhesion, forwithstanding the above described severe conditions, between fluororubberand silicone rubber which are chemically stable and hardly adhere witheach other;

(2) a problem that fluororubber used in the innermost layer lacksflexibility due to its high rigidity; particularly, fluororubber has acommon drawback that, under such high temperatures as ranging from 180to 200° C. which constitute the application conditions of theturbocharger hose, fluororubber becomes brittle and tends to be broken,so that any material remedy may be hardly found and there occurs anissue about what structure is to be adopted;

(3) a problem that fluororubber has a significant drawback that it ishigh in crystallinity, and hence poor in brittle resistance at lowtemperature, resulting in generation of air leakage from the jointportions of the hose at low temperature; and

(4) a problem that fluororubber is a very expensive material, and henceit is critical from the economic viewpoint that the fluororubber layeris formed as thin as possible.

For the purpose of obtaining a practical hose, there are needed measuresto comprehensively solve the above described problems (1) to (4), but nosuch measures are disclosed in the above described publication. Inparticular, the publication describes that the adhesion of fluororubberand silicone rubber to each other “is carried out by a conventionalvulcanization adhesion,” but it is impossible to adhere fluororubber andsilicone rubber to each other by a conventional vulcanization methodunless any special formulation is added to the rubber compounding.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a novel rubberhose which has solved the above described problems and a method formanufacturing the rubber hose.

Another object of the present invention is to provide an improved rubberhose in which the low durability and low adhesiveness of thefluororubber layer is improved and upgraded by arranging a specificintermediate silicone rubber layer between the fluororubber layer andthe outer silicone rubber layer.

A first aspect of the present invention is a rubber hose in which anouter rubber layer is laminated by means of extrusion on the outerperipheral surface of an inner rubber layer, the rubber hose beingcharacterized in that:

the inner rubber layer is a fluororubber layer;

the outer rubber layer is a reinforcing yarn-woven silicone rubber layerhaving reinforcing yarns woven therein;

an intermediate rubber layer containing an adhesive component for theadhesion with the fluororubber layer is provided between thefluororubber layer and the reinforcing yarn-woven silicone rubber layer;and

the intermediate rubber layer is an intermediate silicone rubber layerhaving a hardness lower than those of the reinforcing yarn-wovensilicone rubber layer and the fluororubber layer to be the innermostlayer.

The fluororubber is preferably a terpolymer composed of vinylidenefluoride, hexafluoropropylene and tetrafluoroethylene or a copolymercomposed of tetrafluoroethylene and propylene from the viewpoint of theresistance to the amines contained in the engine oil as an antiagingagent and an antirust.

The rubber hose according to the first aspect is preferably produced bythe following manufacture method.

The method concerned is an extrusion method for manufacturing a rubberhose in which an intermediate silicone rubber layer having a hardnesslower than that of the reinforcing yarn-woven silicone rubber layer isprovided by means of extrusion between the fluororubber layer and thereinforcing yarn-woven silicone rubber layer outside thereof, the methodconcerned being characterized in that:

the fluororubber layer, the intermediate silicone rubber layer and thereinforcing yarn-woven silicone rubber underlayer are extruded in alaminated condition by a first extruder to be fed to a weaving machine;

the weaving machine weaves reinforcing yarns on the outer peripheralsurface of the reinforcing yarn-woven silicone rubber underlayer andthen feeds the laminate to a second extruder; and

the second extruder coats the outer peripheral surface of thereinforcing woven yarn with a reinforcing yarn-woven silicone rubberlayer.

A second aspect of the present invention is a rubber hose in which anouter rubber layer is laminated by means of winding on the outerperipheral surface of an inner rubber layer, the rubber hose beingcharacterized in that:

the inner rubber layer is a fluororubber layer;

the outer rubber layer is a fabric-reinforced silicone rubber layer;

an intermediate silicone rubber layer containing an adhesive componentfor the adhesion with the fluororubber layer is provided between thefluororubber layer and the fabric-reinforced silicone rubber layer; and

the intermediate silicone rubber layer is an intermediate siliconerubber layer having a hardness lower than those of the fabric-reinforcedsilicone rubber layer and the fluororubber layer to be the inner layer.

The rubber hose according to the second aspect is preferably produced bythe following manufacture method.

The method concerned is a winding method for manufacturing a rubber hosein which an intermediate silicone rubber layer having a hardness lowerthan those of the fabric-reinforced silicone rubber layer and the innerfluororubber layer is provided by means of winding between thefluororubber layer and the fabric-reinforced silicone rubber layeroutside thereof, the method concerned being characterized in that:

the fluororubber layer sheet is prepared by use of a calendar roll;

the intermediate silicone rubber is press-coated (or, contact bonded) tothe fluororubber layer sheet to prepare a laminated sheet composed ofthe fluororubber layer sheet and the intermediate silicone rubber layersheet; and

the laminated sheet is wound around a metal mandrel having apredetermined shape, and then a fabric-reinforced silicone rubbertopping sheet, prepared in advance, is wound on the laminated sheet toproduce the rubber hose.

In this case, for the intermediate silicone rubber, a silicone rubberthat is softer in the material hardness thereof than thefabric-reinforced silicone rubber is selected. The fabric-reinforcedsilicone rubber layer (hereinafter referred to as the silicone rubberlayer) sheet as the topping sheet is a sheet in which an aramidreinforcing fabric or the like is incorporated in silicone rubber, andthis sheet may be prepared by a conventional method in which siliconerubber is kneaded with a roll to be thermally plastic and then thesilicone rubber is compression bonded with a calendar roll to eitherboth or one of the surfaces of the fabric while a reinforcing fabric isbeing fed.

In the method for manufacturing the rubber hose in the second aspectaccording to the present invention, silicone rubber is extremely soft,so that it is very difficult to prepare a thin layer of approximately0.1 to 0.3 mm in thickness if the silicon rubber is used alone, butactually, the laminated sheet composed of the fluororubber layer sheetand the intermediate silicone rubber layer sheet is preparedsequentially with a calendar roll, so that the softness of siliconerubber is compensated by the hardness of unvulcanized fluororubber,resulting in the improvement of the workability and the moldability.Consequently, there are also provided such advantages that the thicknessof the fluororubber sheet can be made thin and uniform, and both sheetsare compression bonded to each other under the conditions that softsilicone rubber is being thermally softened, so that the mutual adhesionof both sheets is elevated and the air incorporated therebetween can beeliminated. According to this method, the fluororubber layer sheet canbe made as extremely thin as 0.1 mm, so that this method is morefavorable than the extrusion from the viewpoint of the cost.

As described above, fluororubber is hard and lacks flexibility, and inparticular, when it undergoes large vibrations at high temperatures andstress concentration, it tends to be broken. Accordingly, when theintermediate silicone rubber layer composed of the silicone rubberhaving a hardness lower than those of the silicone rubber constitutingthe reinforcing yarn-woven (or fabric-reinforced) silicone rubber layerand the fluororubber constituting the inner fluororubber layer isprovided between the fluororubber layer and the reinforcing yarn-woven(or fabric-reinforced) silicone rubber layer, the intermediate siliconerubber layer works as a shock absorber to disperse the stress exerted onthe inner fluororubber layer. Also, the adhesion concerned is the onebetween the soft and same quality materials, as compared to the casewhere the fluororubber layer and the silicone rubber layer are directlyadhered to each other, so that better adhesive force can be obtained.The adhesive component is needed to be mixed only in the intermediatesilicone rubber layer, the mixed amount of the adhesive component can bemade small in an economically efficient manner. Also, becausefluororubber is poor in brittle resistance at low temperature, sealingproperties at low temperatures are lowered, for instance, when acounterpart pipe is inserted into the hose; however, the lamination ofthe intermediate silicone rubber layer excellent in brittle resistanceat low temperature on such fluororubber layer improves the sealingproperties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating an example of a rubber hoseaccording to a first embodiment of the present invention;

FIG. 2A is a schematic block diagram illustrating a preferable methodfor manufacturing the rubber hose shown in FIG. 1;

FIG. 2B is a schematic block diagram illustrating another preferablemethod for manufacturing the rubber hose shown in FIG. 1;

FIG. 3 is a schematic view illustrating an example of the rubber hosewith ribs formed in the joining portion to a counterpart pipe, shown inFIG. 1 or presented in a second embodiment shown in FIG. 4;

FIG. 4 is a schematic view illustrating an example of a rubber hoseaccording to a second aspect of the present invention;

FIG. 5 is a schematic block diagram illustrating a preferable method formanufacturing the rubber hose shown in FIG. 4; and

FIGS. 6 and 7 each are a schematic view illustrating the embossmentformed on the rubber hose shown in FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

A rubber hose according to a first embodiment of the present inventionwill be described below with reference to FIGS. 1 to 3.

Basically, the rubber hose concerned is a rubber hose in which an outerrubber layer is laminated by means of extrusion on the outer peripheralsurface of an inner rubber layer, wherein the inner rubber layer is afluororubber layer 2, and the outer rubber layer is a reinforcingyarn-woven silicone rubber layer 1 with reinforcing yarns woven therein.The rubber hose has a structure in which an intermediate rubber layer 3having an adhesive component for the adhesion with the fluororubberlayer 2 is provided between the fluororubber layer 2 and the reinforcingyarn-woven silicone rubber layer 1, and the intermediate rubber layer 3is an intermediate silicone rubber layer having a hardness lower thanthose of the reinforcing yarn-woven silicone rubber layer 1 and thefluororubber layer 2.

The basic matters of the rubber hose according to the first embodimentof the present invention are as described above, but when the followingadditional measures are applied, the functions and the properties of therubber hose are further elevated, and accordingly, the followingmeasures will be described below with reference to FIGS. 1, 2A and 2B.

Such a rubber hose can be produced as described above by extrusion, andmore specifically, the extrusion itself may adopt any common extrusionmethod. In other words, a central mandrel (not shown) is adopted for thepurpose of ensuring the accuracy of the inside diameter and preventingthe deformation of the unvulcanized rubber hose; the central mandrel isprovided to any one of three extruders (only one of them is shown)actually constituting a first extruder 10, and thus the first extruder10 extrudes, to the outer peripheral surface of the mandrel, thefluororubber layer 2, the intermediate silicone rubber layer 3 and thereinforcing yarn-woven silicone rubber underlayer 1 a in a laminatedcondition.

A laminate extruded from the first extruder 10 is fed into a weavingmachine 11, and the weaving machine 11 weaves heat resistant fiber suchas aramid fiber on the outer peripheral surface of the reinforcingyarn-woven silicone rubber underlayer 1 a as the outermost layer of thelaminate. The types of the reinforcing yarn braiding with the braidingmachine 11 may include various types such as braid, spiral and knitweavings, similarly to conventional cases. Extrusion is carried outwhile a silicone rubber upper layer 1 c is being laminated on the outerperipheral surface of the reinforcing woven yarn 1 b. In this case, oneor both of the reinforcing woven yarn and the silicone rubber upperlayer may be formed appropriately in multilayer forms according to therequirements involving pressure resistance and the like, similarly toconventional cases. The laminate continuously extruded is cut to arequired length, the central mandrel is taken out, thereafter a mandrelfor use in vulcanization is inserted instead to apply a predeterminedvulcanization treatment and the like, and thus, a desired product isobtained.

In some cases, a silane coupling agent selected as adhesive is appliedonto the outer peripheral surface of the fluororubber layer 2. In thiscase, the extrusion of the fluororubber layer 2, the intermediatesilicone rubber layer 3 and the reinforcing yarn-woven silicone rubberunderlayer 1 a by the first extruder 10 may be divided into twoextrusions, namely, an upstream extrusion and a downstream extrusion, asshown in FIG. 2B, in such a way that the fluororubber layer is extrudedby an upstream, first extruder 10 a, subsequently the silane couplingagent is applied thereon by a silane coupling agent applicator 13, andafter the fluororubber layer is passed through a dryer 14, an extrusionoperation of the intermediate silicone rubber layer 3 and thereinforcing yarn-woven silicone rubber underlayer 1 a by a downstream,first extruder 10 b may be carried out.

In the rubber hose thus produced, the thickness of the fluororubberlayer required to be heat resistant and oil resistant is suitably 0.2 to1.5 mm in consideration of the durability and the economic efficiency.The lower thickness limit of 0.2 mm is a limit due to extrusion, and maybe of the order of 0.1 mm if possible. Fluororubber is hard and lacksflexibility in nature, and further has a drawback that the strengththereof at high temperatures is weak. Under such conditions that, asdescribed above, the temperature is as high as 200° C. and vibrationsare exerted, there is a fear that the tensile strength againstelongation is degraded to cause failure. Also, when the fluororubberlayer 2 is thinner than necessary, the rigidity of the rubber hose isincreased by the hardening at low temperatures, and the sealingproperties, the vibration-absorbing properties and the like are not ableto exhibit their original performances. In order to solve such problems,the thickness of the fluororubber layer is critical, so that the abovedescribed range is appropriate.

Table 1 shows the results of the vibration endurance test (observationof the generation of cracks) at 180° C. with variable thickness ofvarious fluororubber layers 2; in any case, when the thickness exceeds1.5 mm, the vibration endurance is degraded. In Table 1, ◯ signifies nogeneration of cracks, Δ signifies the generation of small cracks (0.05mm or less in depth), and X signifies the generation of large cracks(more than 0.05 mm in depth). TABLE 1 Thickness (mm) 0.2 0.5 1.0 1.2 1.52.0 2.5 Fluororubber A ◯ ◯ ◯ ◯ ◯ X X Fluororubber B ◯ ◯ ◯ ◯ ◯ Δ XFluororubber C ◯ ◯ ◯ ◯ ◯ Δ XFluororubber A: Manufactured by hardness (JIS A): 70 Asahi Glass Co.,Ltd.Fluororubber B: Manufactured by hardness (JIS A): 70 Sumitomo 3M Ltd.Fluororubber C: Manufactured by hardness (JIS A): 70 Daikin Industries,Ltd.

It may be noted that, as the above described fluororubber, there wasused any one of a terpolymer (fluororubber B or C) composed ofvinylidene fluoride, hexafluoropropylene and tetrafluoroethylene and acopolymer composed of tetrafluoroethylene and propylene (fluororubberA).

The intermediate silicone rubber layer 3 which is provided between thefluororubber layer 2 and the reinforcing yarn-woven silicone rubberlayer 1 (hereinafter referred to as silicon rubber layer 1) andfunctions as the shock absorber for these two layers has, as preferableconditions, a hardness lower than those of the silicone rubber layer 1and the fluororubber layer 2. More specifically, the hardness of theintermediate silicone rubber layer is suitably lower by 10 to 30 interms of the JIS A hardness. The thickness of the intermediate siliconerubber layer 3 is suitably 0.3 to 2 mm. For the purpose of making theintermediate silicone rubber layer 3 to take over the stress exerted onthe fluororubber layer 2, the thickness of the intermediate siliconerubber layer 3 is required to be 0.3 mm or more, but must not be toolarge and is suitably 2 mm or less. The thickness exceeding this is notpreferable because such a thickness leads to the compression settlingaround the portion beneath the fastening band arranged along the outerperipheral surface of the silicone rubber layer 1. An adhesive componentis mixed in the intermediate silicone rubber layer 3, and if thethickness thereof is increased, the mixed amount of the adhesive is alsoincreased to raise the price. This is also another drawback.

It is also effective to mix aramid staple fiber in the fluororubberlayer 2. Fluororubber is degraded in strength at high temperatures, andthe mixing of such a heat resistant staple fiber makes it possible toprevent the strength degradation. Such a staple fiber attains anchoringeffect to improve the adhesion. The mixed amount of aramid staple fiberis suitably 5 to 40 parts by weight in relation to the 100 parts byweight of the starting material polymer (hereinafter, this will berepresented as “5 to 40 PHR”). When the mixed amount of aramid staplefiber falls outside this range, the above described functions aredegraded. Examples of the usable aramid staple fibers may includearomatic polyaramids such as polyparaphenylene isophthalamide andpolymetaphenylene isophthalamide.

It has been revealed that when silicone oil is mixed in the fluororubberlayer 2, the elongation properties are improved, and the durability isalso improved. As this silicone oil, (1) polymethylsilicone, (2)polymethylphenylsilicone and the like can be used. The mixed amount ofsilicone oil is suitably 0.5 to 10 PHR. When the mixed amount is lessthan 0.5 PHR, the advantageous effect of silicone oil is small, whilewhen the mixed amount exceeds 10 PHR, adhesion failure occurs. Thus,usually, the mixed amount is suitably 1 to 3 PHR. Table 2 presentedbelow shows the relation between the mixed amount and the elongationindex. TABLE 2 Fluororubber without silicone oil (1) 3 PHR (2) 3 PHRElongation index 100 130 150

Mixing of magnesium oxide in the intermediate silicone rubber layer 3 isalso preferable because this mixing improves the adhesion. In general,amine-vulcanized fluororubber and polyol-vulcanized fluororubber aremixed with magnesium oxide as acid acceptor; if magnesium oxide is alsomixed in the intermediate silicone rubber layer 3, namely, a layer to beadhered, it can be seen that adhesion is improved. The mixed amount ofmagnesium oxide is suitably 2 to 15 PHR. When the mixed amount is lessthan 2 PHR, advantageous effects are small, while when the mixed amountexceeds 15 PHR, the intermediate silicone rubber layer 3 is hardened andunpreferably the durability is decreased. Table 3 presented below showsthe relation between the mixed amount of magnesium oxide and theadhesion. TABLE 3 Mixed amount (PHR) 0 2 10 15 20 Adhesion X Δ ◯ ◯Hardening failureX: Interface failure;Δ: Partial interface failure;◯: Material failure

It has been found that in the case where the fluororubber layer 2 is ofthe peroxide vulcanization type, when triallyl isocyanurate is mixed inthe intermediate silicone rubber layer 3, the adhesion strength isimproved. The mixed amount thereof is suitably 1 to 15 PHR; when themixed amount is less than 1 PHR, advantageous effects are small, whilewhen the mixed amount exceeds 15 PHR, unpreferably scorch and viscosityincrease are caused. Table 4 presented below shows the relation betweenthe mixed amount and the adhesion depending on the fluororubber types.Here, the fluororubber types and the evaluation symbols are the same asdefined for Table 3 (also, the same as in Table 5). TABLE 4 Mixed amount(PHR) Unmixed 1 5 10 15 20 Fluororubber B X Δ ◯ ◯ ◯ HardenedFluororubber C X ◯ ◯ ◯ ◯ Hardened

It has also been found that when a silane coupling agent is mixed in theintermediate silicone rubber layer 3, the adhesive force is increased.Such a silane coupling agent has preferably an organic functional group,such as an amino or epoxy groups. The mixed amount thereof is suitably0.5 to 15 PHR; when the mixed amount is less than 0.5 PHR, advantageouseffects are small, while when the mixed amount exceeds 15 PHR,unpreferably scorch is caused. Table 5 presented below shows therelation between the mixed amount of an aminosilane and the adhesiondepending on the fluororubber types. TABLE 5 Mixed amount (PHR) Unmixed0.2 0.5 2 5 10 15 Fluororubber B X X Δ ◯ ◯ ◯ Hardened Fluororubber C X ◯◯ ◯ ◯ ◯ Hardened

When the rubber hose is practically used under the conditions that thetemperature is as high as 200° C. and additionally the rubber hoseundergoes vibration, there occurs a phenomenon that the fluororubberlayer 2 and the counter part pipe (not shown) connected to the hose arethermally fixed to each other to make the detachment thereof difficult.For the purpose of preventing such a phenomenon, it is effective toapply a release agent onto the inner peripheral surface of thefluororubber layer in the joining portion 2. This is because theapplication of a release agent reduces the dynamic friction coefficientto suppress the fixation. Among various release agents, silicone releaseagents are preferable because of the high releasing effect thereof.Because, for the purpose of attaining required functions to a fullextent, this kind of hoses are usually subjected to post-vulcanizationunder conditions of about 5 hours at about 200° C., there is usuallyadopt a procedure in which the release agent is applied with a brush orthe like before this operation, and thermally fixed in thepost-vulcanization.

Table 6 presented below shows a comparison of the detachment properties(anti-fixing properties) of the case where a release agent treatment wascarried out by use of a baking-type silicone release agent HS-1(manufactured by Toshiba Silicone Co., Ltd.) and the case where no sucha treatment was carried out; the application of the release agentdrastically improved the dynamic friction coefficient to permitdetachment only by manual pulling. TABLE 6 Anti-fixing propertiesDynamic friction coefficient Not applied X 1 Applied ◯ 0.3X: Fixing is very strong, and detachment requires a release jig.◯: Detachable only by manual pullingConditions: A counterpart pipe made of aluminum was chosen, and a bandfastening test was carried out at 200° C. for 168 hours; thereafter, thefixing properties were evaluated.

As measures against the above described cracking, it is effective toprovide ribs (see reference numeral 7 in FIG. 3) along thecircumferential direction in a protruding manner on the inner peripheralsurface of the fluororubber layer in the joining portion 2. These ribscan be formed by use of a central mandrel with a rib-shaped end portion.When this rubber hose is fastened by a fastening band, the fluororubberlayer 2 is elongated along the longitudinal direction of the hose;however, if ribs 7 are provided in a protruding manner, the ribs 7 worksas a compensation for the elongation, and the generation of cracks canthereby be prevented. The ribs 7 are provided along the circumferentialdirection, so as not to affect the sealing properties; when the numberof the ribs 7 formed in this case is two or more, higher effects areattained. In addition, this structure reduces the contact surface areawith the counterpart pipe, so as to be effective in preventing thefixation.

Table 7 presented below shows the results of the investigations of thegeneration of cracks when fastening is made with a fastening band byadopting a rubber hose in which a plurality of 0.5 mm high and 3 mm wideribs 7 are formed in a protruding manner on the inner peripheral surfaceof the joining portion of the rubber hose and a rubber hose without suchribs. The effects of the application of the above described releaseagent were also simultaneously investigated; it has been found that theprovision of the ribs 7 can suppress the cracking and the application ofa release agent further improves the fixing properties. The fasteningtorque of the fastening band was set at 10 N-m; for an usual fasteningtorque of about 5 N-m, application of the above described procedures cansuppress the cracking; thus, it is a very significant effect that thecracking and the fixation were not caused even by applying such moresevere and harsh fastening conditions as 10 N-m. TABLE 7 Application ofAnti-fixing Ribs release agent Cracking properties Rubber None NoMicro-cracking X hose (1) Rubber Present No No ◯ hose (2) Rubber PresentYes No ⊚ hose (3)

In the evaluation of the anti-fixing properties in Table 7, the symbols“X and ◯” are the same as described above, and the symbol “⊚” means acondition in which detachment can be made only by manual pulling.

A method may be cited in which, for the purpose of ensuring the adhesionbetween the fluororubber layer 2 and the intermediate silicone rubberlayer 3, an organosilane adhesive containing as the main componentthereof a silane coupling agent is applied on the outer peripheralsurface of the fluororubber layer in place of or in combination with theabove described methods for improving the adhesion concerned. Thisapplication can be carried out automatically in the extrusion in suchaway that the extrusion, by the first extruder 10, of the fluororubberlayer 2, the intermediate silicone rubber layer 3 and the siliconerubber underlayer 1 a is divided, as FIG. 2B shows, into the extrusionof the fluororubber layer 2 by the upstream, first extruder 10 a, theapplication of the silane coupling agent by the silane coupling agentapplicator 13, and the extrusion of the intermediate silicone rubberlayer 3 and the silicone rubber underlayer 1 a by the downstream, firstextruder 10 b. According to this way, the adhesion between thefluororubber layer 2 and the intermediate silicone rubber layer 3 isimproved. As the organosilane adhesive, Chemlock S-2, Chemlock S-10A,Megum 3290-1 and the like are used. These adhesives are available asalcohol solutions, a spray applicator may be used.

Example 1

There were produced a rubber hose (Y) and a rubber hose (Z) by use ofthe above described fluororubber B for the fluororubber layer 2, therubber hose (Y) being provided with the intermediate silicone rubberlayer 3 between the fluororubber layer 2 and the silicone rubber layer1, and in the rubber hose (Z), the intermediate silicone rubber layer 3being omitted to leave the silicone rubber layer 1 as only one siliconerubber layer. In the production of the rubber hose (Y), as shown in FIG.2A, a laminate composed of the fluororubber layer 2, the intermediatesilicone rubber layer 3 and the silicone rubber layer 1 (JIS A hardness:70) was produced by means of the method based on the first extruder 10,the weaving machine 11 and the second extruder 12. In the production ofthe rubber hose (Z), the intermediate silicone rubber layer was omitted.Here, each of the fluororubber layers was set at 0.3 mm in thickness;and the intermediate silicone rubber layer 3 had a JIS A hardness of 50,contained magnesium oxide in a content of 5 PHR and trially isocyanuratein a content of 10 PHR, and was set at 1.0 mm in thickness. Thisextruded hose was cut to a predetermined length, the central mandrel wastaken out, a bent mandrel for use in vulcanization which had an outsidediameter of 50 mm and bellows was inserted, then the whole outerperipheral surface of the hose was wound with a heat shrinkable tape;the thus treated hose was placed in a boiler, and it was vulcanized at165° C. for 30 minutes to shape. After completion of the vulcanization,the tape was unwound and the hose was placed in a thermostatic oven tobe subjected to a secondary vulcanization at 200° C. for 5 hours for thepurpose of attaining appropriate physical properties. The abovedescribed rubber hoses (Y) and (Z) produced in this way each werefastened with a band by exerting a torque of 5 N-m, and were subjectedto a heat resistant durability test at 180° C., resulting in anobservation that the rubber hose (Y) did not exhibit any abnormality,but the rubber hose (Z) exhibited cracks in the portion of thefluororubber layer 2 beneath the fastening band. Thus, the effectivenessof the intermediate silicone rubber layer 3 was confirmed.

As described above, in the rubber hose in which the fluororubber layer 2and the silicone rubber layer 1 are laminated, when the intermediatesilicone rubber layer 3 composed of a silicone rubber having a hardnesslower than those of the silicone rubber constituting the silicone rubberlayer 1 and the fluororubber constituting the fluororubber layer 2 isprovided between the fluororubber layer 2 and the silicone rubber layer1, the intermediate silicone rubber layer 3 works as a shock absorber todisperse the stress exerted on the fluororubber layer 2; also becausethe intermediate silicone rubber layer 3 is soft, it enhances theadhesion with the fluororubber layer 2. Also, because the adhesive isneeded to be mixed only in the intermediate silicone rubber layer 3, themixed amount of the adhesive can be made small in an economicallyefficient manner.

Second Embodiment

A rubber hose according to a second embodiment of the present inventionwill be described below with reference to FIGS. 3 to 7.

As shown in FIGS. 4 to 7, the rubber hose according to the secondembodiment is a rubber hose in which an outer rubber layer is laminatedby means of winding on the outer peripheral surface of an inner rubberlayer, the rubber hose having a structure in which the inner rubberlayer is a fluororubber layer 5 and the outer rubber layer is afabric-reinforced silicone rubber layer 4; an intermediate rubber layer6 containing an adhesive component for the adhesion with thefluororubber layer 5 is provided between the fluororubber layer 5 andthe fabric 4 a-reinforced silicone rubber layer 4; and the intermediaterubber layer 6 is made to be a intermediate silicone rubber layer 6having a hardness lower than those of the fabric-reinforced siliconerubber layer 4 and the fluororubber layer 5.

The basic matters of the second embodiment of the present invention areas described above, but when the following additional measures areapplied, the functions and the properties of the rubber hose are furtherelevated. The details of the measures are as follows, being not muchdifferent from those described above for the case of the firstembodiment.

The thickness of the fluororubber layer 5 required to be heat resistantand oil resistant is suitably 0.1 to 1.5 mm in consideration of thedurability and the economic efficiency. Fluororubber is hard and lacksflexibility in nature, and further has a drawback that the strengththereof at high temperatures is weak. Under such conditions that, asdescribed above, the temperature is as high as 200° C. and vibrationsare exerted, there is a fear that the tensile strength againstelongation is degraded to cause failure. For the purpose of solving thisproblem, the thickness of the fluororubber layer is critical, and theabove described range is suitable; as described above, in the windingmethod, the fluororubber layer 5 can be made to be a thin layer with acalender roll in such a way that a hose having a 0.1 to 0.5 mm thickfluororubber layer 5 can be produced advantageously in cost.

In addition to the above descriptions, the various experimental results(Tables 1 to 7) described in relation to the first embodiment and thedescriptions associated therewith are also applicable to the case of thesecond embodiment. As described above, for the purpose of ensuring theadhesion between the fluororubber layer 5 and the intermediate siliconerubber layer 6, available methods include a method in which anorganosilane adhesive containing as the main component thereof acoupling agent is applied on the outer peripheral surface of thefluororubber sheet when a laminated sheet is produced by use of acalender roll; because this adhesive is available as an alcoholsolution, the above purpose can be attained by uniform applicationthereof onto the fluororubber layer 5 sheet with a spray.

It is also preferable to form embossment as shown in FIGS. 6 and 7 whenthe outer peripheral surface of the fluororubber layer 5, facing theintermediate silicone rubber layer 6, is processed with a calendar roll.The fluororubber layer 5 is compatible with embossing, and theembossment formation thereon can be achieved with a common embossing. Inthis way, the surface area is increased and the anchoring effect of theembossment can also be expected to provide an effect that the adhesionbetween unvulcanized fluororubber and silicone rubber is increased andthe adhesive force after vulcanization is thereby further increased.

Additionally, ribs 7 similar to the ribs (reference numeral 7 in FIG. 3)formed in the first embodiment can also be formed on the fluororubberlayer 5 of the second embodiment (see FIG. 3). The fabrication methodthereof and the operation and the advantageous effects thereof are thesame as in the above described first embodiment.

The examples based on the second embodiment will be described below asExamples 2, 3 and 4.

Example 2

Performance tests were carried out on a rubber hose (Y) and a rubberhose (Z) in each of which the above described fluororubber B was usedfor the fluororubber layer 5, in the rubber hose (Y), a silicone rubbercontaining an amino silane in a content of 2 PHR and having a JIS Ahardness of 40 for the intermediate silicone rubber layer 6, and in therubber hose (Z), the intermediate silicone rubber layer 6 being omittedto leave the silicone rubber layer as only one silicone rubber layer. Asshown in FIG. 5, in the production of these rubber hoses, a fluororubbersheet is prepared (reference numeral 20), and the fluororubber layer 5and the intermediate silicone rubber layer 6 were laminated with acalendar roll, resulting in a thickness of 0.2 mm for the fluororubberlayer 5 and a thickness of 1.0 mm for the intermediate silicone rubberlayer 6. The topping sheet for forming the silicone rubber layer wasprepared as a 1.5 mm thick laminated sheet by press-coating (referencenumeral 21) a silicone rubber having a JIS A hardness of 65 onto bothsurfaces of a meta aramid fabric. A laminated sheet composed of thefluororubber layer 5 sheet and the intermediate silicone rubber layer 6sheet was wound around an iron bent mandrel which had an outsidediameter of 85 mm and bellows, thereafter the topping sheet for thesilicone rubber layer was wound triply (reference numeral 22), and thenthe whole outer peripheral surface of the hose was wound with ashrinkable tape; the thus treated hose was placed in a steam chamber,and it was vulcanized at 165° C. for 30 minutes. After completion of thevulcanization, the tape was unwound and the hose was placed in a hot-airoven to be subjected to a secondary vulcanization at 200° C. for 5 hoursfor the purpose of attaining appropriate physical properties. The abovedescribed rubber hoses (Y) and (Z) produced in this way each weresubjected to a durability test at 180° C., and the results obtained werecompared. According to the results, the rubber hose (Y) did not exhibitany abnormality, but the rubber hose (Z) exhibited cracks in the portionof the fluororubber layer beneath the fastening band. Thus, theeffectiveness of the intermediate silicone rubber layer was confirmed.

Example 3

Performance tests were carried out on a rubber hose (1) in which theabove described fluororubber C was used for the fluororubber layer 5 anda silicone rubber having a JIS A hardness of 50 and containing magnesiumoxide in a content of 7 PHR was used for the intermediate layer 6, and arubber hose (2) in which no magnesium oxide was contained. In this case,the thickness of the fluororubber layer was set at 0.2 mm, the thicknessof the intermediate silicone rubber layer was set at 0.5 mm, and thevulcanization and shaping of the topping sheet to be the silicone rubberlayer and the hoses were carried out in the same manner as in abovedescribed Example 2. The above described rubber hoses (1) and (2)produced in this way each were subjected to the same durability test asdescribed above, and the results obtained were compared. According tothe results, the rubber hose (1) did not exhibit any abnormality overthe whole area thereof, but the rubber hose (2) exhibited separation ina portion of the fluororubber layer 5 beneath the fastening band and inthe ends of the hose. Thus, the effectiveness of magnesium oxide wasconfirmed.

Example 4

Two hoses were produced in the same manner as in Example 2; one was ahose in which a 0.2 mm thick layer of the above described fluororubber C(JIS A hardness: 60) was used for the fluororubber layer 5, a material(JIS A hardness: 45) in which a basic formulation further containedpolymethylsilicone oil in a content of 3 PHR and magnesium oxide in acontent of 10 PHR was used for the 1.0 mm thick intermediate siliconerubber layer 6, and a fabric-reinforced silicone rubber sheet (JIS Ahardness: 65; total thickness: 1.3 mm) was wound therearound in triplelayers, and the other was a hose which did not include the intermediatesilicone rubber 5.

On these two hoses, a low-temperature seal durability (at −40° C., withrepeated cycles of the internal pressure variation from 0 to 250 kPa)test was carried out with 50 g of an engine oil placed inside each ofthe hoses. Consequently, without the intermediate silicone rubber layer5, oil bleed leakage was caused from the end portions, but with theintermediate silicone rubber layer 5, absolutely no leakage was found.Thus, the low-temperature drawback of fluororubber was compensated bythe intermediate-layer silicone rubber which is excellent in brittleresistance at low temperature and has flexibility, and consequentlyexcellent properties were able to be attained.

As described above, also in the case of the rubber hose according to thesecond embodiment in which the fluororubber layer 5 and the siliconerubber layer 4 were laminated, similarly to the above described firstembodiment, placement of the intermediate silicone rubber layer 6between the fluororubber 5 and the silicon rubber 4, where theintermediate layer is composed of a silicone rubber having a hardnesslower than those of the silicone rubber constituting the silicone rubberlayer 4 and the fluororubber, enables the intermediate silicone rubberlayer 6 work to as a shock absorber, disperse the stress exerted on thefluororubber layer 5, and make the fluororubber layer of the hosethinner. The intermediate silicone rubber layer 6 enhances the adhesionwith the fluororubber layer 5 to result in an enhancement of theadhesion of the layers by an adhesive, and the adhesive is needed to bemixed only in the intermediate silicone rubber layer 6, the mixed amountof the adhesive can be made small in an economically efficient manner.

1. A rubber hose having an outer rubber layer laminated by means ofextrusion on the outer peripheral surface of an inner rubber layer,wherein: the inner rubber layer is a fluororubber layer; the outerrubber layer is a reinforcing yarn-woven silicone rubber layer havingreinforcing yarns woven therein; an intermediate rubber layer having anadhesive component for the adhesion with said fluororubber layer isprovided between said fluororubber layer and said reinforcing yarn-wovensilicone rubber layer; and the intermediate rubber layer is anintermediate silicone rubber layer having a hardness lower than those ofsaid reinforcing yarn-woven silicone rubber layer and said fluororubberlayer.
 2. The rubber hose according to claim 1, in which thefluororubber comprises a terpolymer of vinylidene fluoride,hexafluoropropylene and tetrafluoropropylene or a copolymer oftetrafluoroethylene and propylene.
 3. The rubber hose according to claim1, in which the thickness of the fluororubber layer is set at 0.2 to 1.5mm.
 4. The rubber hose according to claim 1, in which the materialhardness of the intermediate silicone rubber layer is lower by 10 to 30in terms of the JIS A hardness than those of the reinforcing yarn-wovensilicone rubber layer and the innermost fluororubber layer.
 5. Therubber hose according to claim 1, in which the thickness of theintermediate silicone rubber layer is set at 0.3 to 2 mm.
 6. The rubberhose according to claim 1, in which the fluororubber layer comprises 5to 40 parts by weight of aramid staple fibers in relation to 100 partsby weight of the raw material polymer.
 7. The rubber hose according toclaim 1, in which the fluororubber layer comprises 0.5 to 10 parts byweight of a silicone oil in relation to 100 parts by weight of the rawmaterial polymer.
 8. The rubber hose according to claim 1, in which theintermediate silicone rubber layer comprises 2 to 15 parts by weight ofmagnesium oxide in relation to 100 parts by weight of the raw materialpolymer.
 9. The rubber hose according to claim 1, in which theintermediate silicone rubber layer comprises 1 to 15 parts by weight oftriallyl isocyanurate in relation to 100 parts by weight of the rawmaterial polymer.
 10. The rubber hose according to claim 1, in which theintermediate silicone rubber layer comprises 0.5 to 10 parts by weightof a silane coupling agent in relation to 100 parts by weight of the rawmaterial polymer.
 11. The rubber hose according to claim 1, in which asilicone release agent is applied onto the inner peripheral surface ofthe fluororubber layer in the joining portion to a counterpart pipe tobe inserted therein.
 12. The rubber hose according to claim 1, in whicha plurality of ribs are provided along the circumferential direction ina protruding manner on the inner peripheral surface of the fluororubberlayer in the joining portion to a counterpart pipe to be insertedtherein.
 13. The rubber hose according to claim 1, in which anorganosilane adhesive is applied between the fluororubber layer and theintermediate silicone rubber layer.
 14. A method for manufacturing arubber hose by means of extrusion in which an intermediate siliconerubber layer is provided between a fluororubber layer and a reinforcingyarn-woven silicone rubber layer outside thereof, the intermediate layerhaving a hardness lower than those of the reinforcing yarn-wovensilicone rubber layer and the innermost fluororubber layer, wherein: thefluororubber layer, the intermediate silicone rubber layer containing anadhesive component for the adhesion with said fluororubber layer, theintermediate layer having a hardness lower than those of saidfluororubber and said reinforcing yarn-woven silicone rubber outsidethereof, and the reinforcing yarn-woven silicone rubber underlayer areextruded in a laminated condition by a first extruder to feed theresulting laminate to a weaving machine; the weaving machine weavesreinforcing yarns on the outer peripheral surface of the reinforcingyarn-woven silicone rubber underlayer to feed the woven laminate to asecond extruder; and the second extruder coats the outer peripheralsurface of the reinforcing woven yarns with a reinforcing yarn-wovensilicone rubber upper layer.
 15. The method for manufacturing a rubberhose according to claim 14, in which the reinforcing woven yarns and/orthe silicone rubber upper layer are formed in multilayer forms.
 16. Themethod for manufacturing a rubber hose according to claim 14, in which asilane coupling agent is applied onto the outer peripheral surface ofthe fluororubber layer, wherein: the lamination by the first extruder ofthe fluororubber layer, the intermediate silicone rubber layer having ahardness lower than those of said fluororubber layer and saidreinforcing yarn-woven silicone rubber layer and the reinforcingyarn-woven silicone rubber underlayer is carried out by: extrusion ofthe fluororubber layer by an upstream, first extruder; application ofthe silane coupling agent by a silane coupling agent applicator; andextrusion of the intermediate silicone rubber layer and the reinforcingyarn-woven silicone rubber underlayer by a downstream, first extruder.17. A rubber hose having an outer rubber layer laminated by means ofwinding on the outer peripheral surface of an inner rubber layer,wherein: the inner rubber layer is a fluororubber layer; the outerrubber layer is a fabric-reinforced silicone rubber layer; anintermediate silicone rubber layer containing an adhesive component forthe adhesion with the fluororubber layer is provided between thefluororubber layer and the fabric-reinforced silicone rubber layer; andthe intermediate rubber layer is an intermediate silicone rubber layerhaving a hardness lower than those of the fabric-reinforced siliconerubber layer and said fluororubber layer to be the innermost layer. 18.The rubber hose according to claim 17, in which the fluororubber iscomposed of a terpolymer of vinylidene fluoride, hexafluoropropylene andtetrafluoropropylene or a copolymer of tetrafluoroethylene andpropylene.
 19. The rubber ho se according to claim 17, in which thethickness of the fluororubber layer is set at 0.2 to 1.5 mm.
 20. Therubber hose according to claim 17, in which the material hardness of theintermediate silicone rubber layer is lower by 10 to 30 in terms of theJIS A hardness than those of the reinforcing yarn-woven silicone rubberlayer and the fluororubber layer.
 21. The rubber hose according to claim17, in which the thickness of the intermediate silicone rubber layer isset at 0.3 to 2 mm.
 22. The rubber hose according to claim 17, in whichthe fluororubber layer comprises 5 to 40 parts by weight of aramidstaple fibers in relation to 100 parts by weight of the raw materialpolymer.
 23. The rubber hose according to claim 17, in which thefluororubber layer comprises 0.5 to 10 parts by weight of a silicone oilin relation to 100 parts by weight of the raw material polymer.
 24. Therubber hose according to claim 17, in which the intermediate siliconerubber layer comprises 2 to 15 parts by weight of magnesium oxide inrelation to 100 parts by weight of the raw material polymer.
 25. Therubber hose according to claim 17, in which the intermediate siliconerubber layer comprises 1 to 15 parts by weight of triallyl isocyanuratein relation to 100 parts by weight of the raw material polymer.
 26. Therubber hose according to claim 17, in which the intermediate siliconerubber layer comprises 0.5 to 10 parts by weight of a silane couplingagent in relation to 100 parts by weight of the raw material polymer.27. The rubber hose according to claim 17, in which a silicone releaseagent is applied onto the inner peripheral surface of the fluororubberlayer in the joining portion to a counterpart pipe to be insertedtherein.
 28. The rubber hose according to claim 17, in which a pluralityof ribs are provided along the circumferential direction in a protrudingmanner on the inner peripheral surface of the fluororubber layer in thejoining portion to a counterpart pipe to be inserted therein.
 29. Therubber hose according to claim 17, in which an organosilane adhesive isapplied between the fluororubber layer and the intermediate siliconerubber layer.
 30. The rubber hose according to claim 17, in whichembossment is formed on the outer peripheral surface of the fluororubberlayer.
 31. (canceled)
 32. A method for manufacturing a rubber hose bymeans of winding in which an intermediate silicone rubber layer having ahardness lower than those of the fabric-reinforced silicone rubber layerand the fluororubber layer and containing an adhesive component for theadhesion with said fluororubber and said fabric-reinforced siliconerubber is provided between the fluororubber layer and thefabric-reinforced silicone rubber layer outside thereof, wherein: thefluororubber layer sheet is prepared by use of a calender roll; theintermediate silicone rubber is press-coated onto the fluororubber layersheet to prepare a laminated sheet composed of the fluororubber layersheet and the intermediate silicone rubber layer sheet; and afabric-reinforced silicone rubber topping sheet, prepared in advance, iswound on the laminated sheet to produce the rubber hose.
 33. The methodfor manufacturing a rubber hose according to claim 32, in which anorganosilane adhesive is applied onto the outer peripheral surface ofthe fluororubber layer, wherein; the organosilane adhesive is appliedafter the fluororubber layer sheet is prepared; and thereafter thelaminated sheet composed of the fluororubber layer sheet and theintermediate silicone rubber layer sheet is prepared by rubbing theintermediate silicone rubber into the fluororubber layer sheet.